Currently, the technology for production of single crystalline semiconductor wafers or substrates involves cutting thin wafers from a single crystalline semiconductor ingot. After cutting, the wafers need to be polished to remove the damage caused by the cutting process. The cutting and polishing processes are expensive and cause a large amount waste of material.
The liquid phase epitaxy (LPE) technique was developed to address these issues and has been used to grow premium quality semiconductor layers from a melt on a substrate at temperatures well below the melting point of the deposited semiconductor. Compared to other epitaxy techniques LPE has a higher growth rate but lower capital cost for both equipment and operation.
Many metals may be used for LPE silicon growth, such as tin, copper, aluminum and indium. A solution of silicon in molten metal is formed. Because indium has a low melting point (156.6° C.), relatively more silicon may be dissolved in liquid indium to form an indium/silicon alloy. Because solubility of silicon in indium decreases with decreasing temperature, when the temperature of silicon-saturated indium melt decreases, the decrease in silicon solubility in indium results in nucleation of silicon and epitaxial growth on the substrate. The maximum indium solubility in silicon is 2.5×1018 atoms/cm−3 at a temperature of 1300° C.
One of the limitations of liquid phase epitaxy is that the epitaxially grown structures are necessarily supported on single crystal substrates. The new wafers, therefore, have to be cut away from the supporting substrate resulting loss of material from cutting and polishing, thereby increasing the production costs. Accordingly, there remains a need for a technique for growing self-supported single crystal semiconductor sheets.